Pressure-compensated flow control

ABSTRACT

Spool valve having its inlet flow rate regulated by a pressurecompensating piston that is reference to the low-pressure return when the valve spool is in its neutral position holding a load. In a first embodiment the valve spool itself carries a ball shuttle valve that determines which motor port of the spool valve is connected to the pressure-compensating piston. In a second embodiment the bypass flow provided by the pressure-compensating piston may go to another load circuit, such as another pressurecompensated spool valve, or to the low-pressure return. In both embodiments, the pressure-compensating piston acts as a load check in the event of inlet pressure failure.

United States Patent [72] Inventor Donald A. Stremple Strongsville, Ohio[2]] Appl. No. 839,844 [22] Filed July 8,1969 [45] Patented Aug. 31,1971 [73] Assignee Eaton Yale & Towne Inc.

Cleveland, Ohio 54] PRESSURECOMPENSATED FLOW CONTROL 12 Claims, 3Drawing Figs. [52] U.S. C1 91/446, 91/448, 137/117, 137/596.13 [51] Int.Cl ..Fl5b 11/08, Fl5b 13/042 [50] Field ofSearch 91/426, 444, 445, 446,448, 468, 44.5 PR, 117; l37/625.69, 538, 596.13, 117, 1 18, 596.13

[56] References Cited UN lTED STATES PATENTS 2,729,233 1/1956 Garmager137/596. 12 X 3,308,844 3/1967 Nelson 137/118 3,398,649 8/1968McMillen.. 137/596 X 3,456,671 7/1969 Stacey 137/118 2,487,520 11/1949Brown 91/444 X 2,549,979 4/1951 Lane 91/444 Primary Examiner-Martin P.Schwadron Assistant Examiner-Irwin C, Cohen Attorney-Teagno & ToddyABSTRACT: Spool valve having its inlet flow rate regulated by apressure-compensating piston that is reference to the lowpressure returnwhen the valve spool is in its neutral position holding a load. In afirst embodiment the valve spool itself carries a ball shuttle valvethat determines which motor port of the spool valve is connected to thepressure-compensating piston. In a second embodiment the bypass flowprovided by the pressure-compensating piston may go to another loadcircuit, such as another pressure-compensated spool valve, or to thelow-pressure return. In both embodiments, the pressurecompensatingpiston acts as a load check in the event of inlet pressure failure.

PATENTED AUG3I 1971 SHEET 2 OF 2 the spool valve.

Various pressure-compensated flow control arrangements have beenproposed heretofore in which a spool valve has its inlet flow rateregulated by a spring-biased pressure-compensating valve operating inresponse to the pressure differential between the spool valve inlet andthe spool valve motor port which passes the inlet flow to the fluidmotor. Commonly, in such flow control arrangements a reference pressurechamber of the pressure-compensating valve is connected to a motor portof the spool valve even when the spool valve is in neutral, at whichtime it may be used to hold the load on the fluid motor by keeping thismotor port blocked. With such arrangements, in order to connect the pumpoutput to the spool valve inlet it may be necessary for the pumppressure to overcome the fluid force exerted on thepressure-compensating valve by this motor port pressure in addition tothe force exerted by the bias spring.

It is a principal object of the present invention to avoid thisdisadvantage by providing a novel and improved flow control arrangementin which the spring-biased pressure-compensat ing valve is referenced toa low-pressure return when the spool valve is in neutral and holding aload at one of its motor ports, so that the pump pressure is required toovercome only the spring bias on the pressure-compensating valve inorder to connect the pump output to the spool valve inlet.

Another object of this invention is to provide a pressurecompensatedflow control in which a pressure-compensating valve is arranged in anovel manner to act as a load check in the event of a failure of theinlet pressure.

Another object of this invention is to provide a pressurecompensateddirectional spool valve having a shuttle valve positioned in the valvespool and operable in response to the pressure differential betweeninternal passages in the spool, which are connected respectively to theinlet and return motor ports of the spool valve, so as to connect theinlet motor port to the reference pressure chamber of thepressure-compensat ing valve for regulating the inlet flow rate throughthe spool valve.

Further objects and advantages of this invention will be apparent fromthe following detailed description of two presently preferredembodiments, which are illustrated in the accompanying drawings.

In the drawings:

FIG. 1 is a longitudinal sectional view through a first embodiment ofthe present flow control arrangement;

FIG. 2 is a similar view showing a second embodiment of the present flowcontrol arrangement; and

FIG. 3 is a fragmentary longitudinal section showing the shuttle valvein the FIG. 2 flow control arrangement.

FIRST EMBODIMENT-FIG. ll

Referring to FIG. 1, a valve body or housing has a main cylindrical bore11 which snugly, but slidably, receives a valve spool 12 which isaxially shiftable in the bore. Thevalve body 10 also has an auxiliarybore 13 extending parallel to its main bore 11 and slidably receiving apressure-compensating valve member 14.

Midway along its length the auxiliary bore 13 in the valve bodycommunicates with an annular inlet port 15 connected to the outlet of apump 9. A short distance to the right of the inlet port 15 in FIG. 1,and separated from the latter by a cylindrical land 13a, the auxiliarybore 13 communicates with a annular controlled flow outlet port 16 whichis connected by a passage 17 to a pair of axially spaced, arcuate inletpassages 18 and 19 leadinginto the main bore 11 in the valve body. Ashort distance to the left of the inlet port 15 in FIG. 1, and separatedfrom the latter by a cylindrical land 13b, the auxiliary bore 13 in thevalve body communicates with an annular bypass outlet port 20 that maybe connected to a return line (not shown) leading back to the sump S orto another load circuit, such as the inlet of a valve similar to the oneshown in FIG. 1,. A short distance to the right of the port 16, andseparated from the latter by a cylindrical land 13d, the auxilia ry bore13 communicates with an enlarged reference pressure chamber 24 that isconnected by a passage 25 to an annular chamber 26 intersecting the mainbore ill midway between the latters inlet passages 18 and 19. Theopposite ends of the intermediate bore 13 are closed by respectivescrew-threaded plugs 27 and 28.

The pressure-compensating valve member M is an elongated piston having acylindrical land. 14b for sealing engagement with the land 13b ofauxiliary bore 13 and an elongated cylindrical land 14a for sealingengagement with the lands 13a and 13d of bore 13. The piston 14 has aninternal longitudinal passage 29 which at its right end in FIG. Icommunicates with the inlet port l5 through radial openings 30. At itsleft end in FIG. 1, the passage 29 communicates through a radial passage31 with an annular recess 32 that intersects bore 13 to the left of port20 and is separated from the latter by a cylindrical land 13c of bore13. Piston 14 presents a cylindrical land 1140 which sealingly engagesthe bore land 130.

With this arrangement, it will be seen that the piston Ml presentsoppositely facing surfaces of equal areas (at recess 32 and chamber 24)which are exposed respectively to the pump pressure and the pressurethen prevailing in chamber 26 which intersects the main bore 1 1.

A coil spring 6 is engaged under compression between the piston 14 andplug 28 to bias the piston to the left, as shown in FIG. 1, so that theleft end of the piston engages the inner end of plug 27. In thisposition of the piston, its land 14b sealingly engages the bore land13b, its land 14a sealingly engages bore lands 13a and 13d, and its land14c sealingly engages the bore land 130. Accordingly, the inlet port 15is blocked by the piston 14 from the controlled flow outlet port 16leading to the inlet passages 18, 19 to the main bore 11 and from thebypass outlet port 20 leading to return.

To the right of its inlet passage 19 the main bore 11 in the valve bodyis intersected by an annular passage 33 connected to a motor port 34 inthe valve body, which is connected to the rod end f acylinder-and-piston fluid motor 35. To the right of this motor passage33, the bore 11 is intersected by an annular passage 36 which isconnected to a return line 23 leading back to the sump S.

The valve spool 12 has on its periphery an annular circumferentialgroove 37 and a longitudinal groove 38 which intersects groove 37 andextends beyond it in both directions axially. In the neutral, centeredposition of the valve spool, as shown in FIG. 1, the annular groove 37in the valve spool registers with the motor passage 33 in the valve bodyand is blocked from both the inlet passage 19 and the return passage 36.

The right half of the valve spool has a longitudinal internal passage 39whose outer end is closed by a plug 40. Passage 39 is intersected by afirst set of radially disposed transverse ports 41 in the valve spoolwhich partially overlap the return passage 36 in the valve body when thevalve spool is in its neutral position, as shown in FIG. 1.

Passage 39 also is intersected by a. second set of radially disposedtransverse ports 42 in the valve spool, which in the neutral position ofthe valve spool, as shown in FIG. 1, are blocked from both the motorpassage 33 and the return passage 36 in the valve body.

In the neutral position of the valve spool, as shown in FIG. 1, itsinternal passage 39 is connected to the return passage 36 in the valvebody by way of the transverse ports 41 in the valve spool, and the motorpassage 33 is blocked from both the inlet passage 19 and the returnpassage 36.

When the valve spool is displaced far enough to the left from itsneutral position, its peripheral grooves 38, 3'7 connect the inletpassage 19 to the motor passage 33, its transverse ports 42 registerwith the motor passage 33 to connect the latter to the internal passage39 in the valve spool, and its transverse ports 41 are blocked from thereturn passage 36.

Conversely, when the valve spool is shifted far enough to the right fromits neutral position, its peripheral grooves 38, 37 connect the motorpassage 33 to the return passage 36, and either the transverse ports 41or 42 in the valve spool register with the return passage 36 to connectthe internal valve spool passage 39 to this return passage.

To the left of its inlet passage 18 the main bore in the valve body isintersected by an annular passage 33a which is connected through a motorport 34a to the head end of the cylinder and piston 35. To the left ofthis motor passage 33a the main bore 11 in the valve body is intersectedby an annular return passage 36a, which is connected to the return' line23.

The left half of the valve spool has an internal longitudinal passage39a, transverse ports 41a and 42a, and peripheral grooves 37a and 38a,which correspond to the similarly numbered internal passage, transverseports and peripheral grooves in the right half of the valve spool. Theleft end of the internal valve spool passage 39a is closed by a plug40a.

In the neutral centered position of the valve spool, as shown in FIG. 1,its annular peripheral groove 37a registers with the motor passage 33ain the valve body and is blocked from both the inlet passage 18 and thereturn passage 36a, the transverse ports 41a in the valve spoolpartially overlap the return passage 36a to connect the internal passage39a in the valve spool to this return passage, and the transverse ports42a in the valve spool are blocked from both the motor passage 33a andthe return passage 36a.

When the valve spool is shifted sufficiently far to the right from itsneutral position, its peripheral grooves 38a, 37a connect the inletpassage 18 in the valve body to the motor passage 33a, its transverseports 42a register with the motor passage 33a to connect this motorpassage to the internal passage 39a in the valve spool, and itstransverse ports 41a are blocked from the return passage 36a.

Conversely, when the valve spool is shifted sufficiently far to the leftfrom its neutral position, its peripheral grooves 38a, 37a connect themotor passage 33a to the return passage 36a, and either the transverseports 41a or 42a in the valve spool register with the return passage 36ato connect the internal passage 38a in the spool to this return passage.I

The valve spool 12 is biased to its neutral position by a coil spring 43which is engaged under compression between a pair of annular washers 44and 45 slidably surrounding the plug 40a beyond the left end of the mainbore 11 in the valve body. Normally, the spring 43 positions the innerwasher 44 abutting against an outwardly facing annular shoulder 46 onthe valve body at the left end of bore 11 and it positions the outerwasher 45 abutting against a snap ring 48 carried by the valve bodyabutting against a snap ring 49 on the valve spool.

When 'the valve spool is displaced axially to the left from its neutralposition, the valve spool shoulder 47 forces washer 44 to the left whilethe outer washer 45 remains against the snap ring 48 on the valve body,thereby further compressing the centering spring 43.

Conversely, when the valve spool is displaced to the right from itsneutral position, the snap ring 49 on the valve spool forces the outerwasher 45 to the right while the inner washer 44 remains against thevalve body shoulder 46, thereby further compressing the centering spring43.

For the purpose of shifting the valve spool 11 axially, a suitableoperating handle (not shown) is pivotally connected to its right'end.

In accordance with one aspect of the present invention, a ball shuttlevalve is connected between the two internal passages 39 and 39a in thevalve spool and the valve body passage 26 which is connected to thereference pressure chamber 24 at one end of the pressure-compensatingvalve piston 14.

As shown in the drawing, the ball valve 50 is loosely disposed in acylindrical recess 51 in the valve body positioned midway between theinner ends of the respective internal passages 39 and 39a in the valvebody and connected to the latter by respective sleeves 52 and 52a.Radial passages 53 connect this recess 51 to the valve body passage 26.The diameter of the ball valve 50 is less than the axial spacing betweenthe inner ends of sleeves 52 and 52a, so that when the ball valvesealingly engages one of these sleeves the other sleeve is in fluidcommunication with the radial passages 53.

OPERATION When the valve spool 12 is in its neutral position andassuming that the pump 16 is off, then spring 6 will position thepressure-compensating piston 14 as shown in FIG. 1, blocking the pumpoutput from the controlled flow outlet port 16 leading to the inletpassages 18, 19 of the spool valve and from the bypass outlet port 20.

A particular advantage of the present arrangement resides in the factthat in the neutral position of the valve spool the reference pressurechamber 24 behindthe pressure-compensating piston 14 is connected to thelow-pressure return 23 by way of valve body passages 25 and 26 and pastthe ball shuttle valve 50 to the internal passages 39 and 39a in thevalve spool, which are connected by the respective sets of transverseports 41 and 41a to the return passages 36 and 36a in the valve body.Under these circumstances, chamber 24 will have substantially nohydraulic pressure therein, and the only pump pressure required to movethe pressure-compensating piston 14 far enough to the right to connectthe inlet port 15 to controlled fiow outlet port 16 is that necessary toovercome the biasing force exerted by spring 6. That is, there issubstantially no hydraulic force at chamber 24 adding to the force ofspring 6, and tending to oppose such opening of thepressure-compensating valve.

This is in contrast to prior systems of this general type in which thereference pressure chamber behind the pressurecompensating piston isconnected to a motor port of the spool valve when the valve spool is inneutral. In such systems, if the spool valve is holding a load at one ofits motor ports, to open the pressure-compensating valve would require apump pressure sufficient to overcome this motor port pressure acting onthe pressure-compensating piston plus the spring force, whereas in thepresent arrangement the pump pressure is required to overcome only thespring force in order to open the pressure-compensating valve.

When the valve spool 11 is displaced axially from its neutral positionto connect either inlet passage 18 or 19 to the respective motor passage33a or 33 and to connect the other motor passage to return, thereference pressure chamber 24 behind the pressure-compensating piston 14will be connected to the motor passage 33 or 33a which is passing theinlet flow to the cylinder and piston 35. This inlet flow motor passagewill be at a slightly higher pressure than the motor passage which isconducting the return flow from the cylinder. The ball shuttle valve 50will respond to this pressure differential and will move over to seatagainst the sleeve 52 or 52a at the inner end of the respective internalspool valve passage 39 or 39a which is then connected to the returnmotor passage, thereby connecting the motor inlet flow passage to thereference pressure chamber 24 of the pressure-compensating valve.

The pressure-compensating piston 14 senses the pressure differentialbetween the pump output pressure (which at this time is essentially thesame as the pressure at passage 17 leading into the spool valve) and thepressure at the motor passage 33 or 330 which is conducting the inletflow to the cylinder and piston 35. That is, the pressure compensatingpiston effectively senses the pressure drop through the inlet flowpassage of the spool valve. It maintains this pressure differentialconstant, thereby maintaining constant the inlet flow rate to thecylinder and piston 35, by bypassing excess flow from its inlet port 15past the land 14b on the pressure-compensating piston 14 to the bypassport 20. Thus, for any given setting of the valve spool 11, if the inletflow rate through the spool valve attemptsto increase, thepressure-compensating piston 14 will move farther to the right and willthereby increase the bypass flow to return so as to eliminate theattempted inlet flow rate increase. The reverse action takes place ifthe inlet flow rate through the spool valve tends to decrease below therate called for by the axial setting of the valve spool 11.

. If the amount of this bypass flow is not sufficient to reduce theinlet flow through the spool valve in accordance with the latterssetting, the continued movement of piston 14 to the right will cause itsland 14b to progressively restrict the fluid flow from the inlet port 15to the controlled flow outlet port 16, thereby providing a series flowrestriction ahead of the spool valve inlet in addition to providing abypass passage to the bypass outlet port 20.

The biasing force exerted by spring 6 may be adjusted simply by turningthe screw-threaded plug in or out.

The inlet flow rate through the spool valve depends, of course, upon theaxial position of the valve spool 12 because the spool positiondetermines the amount of axial overlap between the inner spool groove 38or 380 and the inlet passage 19 or 18. This overlap provides a variablerestriction orifice in the inlet flow passage through the spool valve,and the pressure-compensating piston senses the pressure differentialacross this restriction orifice to regulate the inlet flow rate, asdescribed.

SECOND EMBODIMENT-FIGURES 2 and 3 FIGS. 2 and 3 show a second embodimentof the present invention which in many particulars is essentiallysimilar to the embodiment of FIG. 1. Elements of the valve arrangementof FIGS. 2 and 3 which correspond to the elements of the FIG. 1 valvearrangement have the same reference numerals plus 100, and the detaileddescription of these elements will not be repeated.

Referring to FIG. 2, the spool valve has just a single annular inletpassage 200 connected to the controlled flow outlet passage 117 from thepressure-compensating valve. The respective motor passages 133 and 133aintersect the main bore 111 on opposite sides axially from the inletpassage 200 and are separated from passage 200 by respective cylindricallands 201 and 2010 of the main bore.

To the right of the motor' passage 133, an annular reference pressurepassage 202 intersects the main bore 111, being separated from motorpassage 133 by a cylindrical land 203 of the main bore. Similarly, areference pressure passage 202a intersects the main bore to the left ofthe motor passage 133a, being separated from the latter by a cylindricalland 203a of the main bore.

The right end of the main bore 111 is intersected by an annular returnpassage 136, located to the right of the reference pressure passage 202and separated from the latter by a cylindrical land 204 of the mainbore. This return passage 136 is connected to the return line 123leading back to the sump S. Similarly, the left end of the main bore isintersected by an annular return passage 136a, located to the left ofthe reference pressure passage 202a and separated from the latter by acylindrical land 204a of the main bore. The reference pressure passages202 and 202a are connected through respective passages 205 and 2050 inthe valve body to ball shuttle valve 206, shown in detail in FIG. 3, andhaving an outlet passage 207 connected to the reference pressure chamber124 of the pressure-compensating valve,

Referring to FIG. 3 the ball shuttle valve has a cartridge body 208received in a bore 209 in the valve body 110. This cartridge body has alongitudinal bore 210 and radial openings 211 connecting this bore tothe passage 205 leading from the reference pressure chamber 202 at themain bore 111 of the valve body. The right end of the cartridge body 200in FIG 3 has an enlarged counterbore 212 which intersects and is coaxialwith bore 210. This counterbore snugly receives a flanged sleeve 213whose outer end communicates with the passage 2050 leading from thereference pressure chamber 202a at the main bore 111 of the valve body.

A ball shuttle valve member 214 is loosely received in the counterbore212 between a valve seat provided by the inner end of sleeve 213 and avalve seat provided at the juncture between counterbore 212 and bore210. Between these valve seats the cartridge body has radial openings215 which provide fluid communication between the counterbore 212 andthe valve body passage 207 leading to the reference pressure chamber 124of the pressure-compensating valve.

In the operation of this ball shuttle valve, when the fluid pressure atreference chamber 202 is higher than the fluid pressure atreferencechamber 202a, the fluid pressure differential acting on theball valve member 214 will force it into seating engagement with thevalve seat on the inner end of sleeve 213, thereby connecting passage205 to the passage 207 leading to chamber 124 and blocking passage 205afrom this chamber. Conversely, when the fluid pressure is higher atreference chamber 202a than at reference pressure chamber 202, the ballvalve member 214 will seat against the valve seat at the inner end ofbore 210, thereby connecting passage 205a to chamber 124 and blockingpassage 205 from this chamber.

Referring again to FIG. 2, the valve spool 112 is of solid crosssection, presenting a cylindrical central land 216 for sealingengagement with the lands 201 and 201a of the main bore 111 on eitherside of the inlet passage 200. This spool land has longitudinal meteringslots or notches 217 which open into the motor passage 133 and similarmetering slots or notches 2170 opening into the other motor passage133a.

Spaced to the right of its central land 216, the valve spool presents anintermediatecylindrical land 218' having a metering slot 219 which opensinto the motor passage 133 and a metering slot 220 which opens into thereference pressure passage 202. Spaced to the left of its central land,thezvalve spool presents a second intermediate cylindrical land 210ahaving a metering slot 219a which opens into the motor passage 133a anda metering slot 2200: which opens into the reference pressure passage202a.

The valve spool has a cylindrical land 221a on its right end whichsealingly engages the main bore 111 to the right of the return passage136 and which is sealingly engageable with the bore land 204 betweenpassages 202 and 136 when the spool is displaced axially to the leftfrom the neutral position shown in FIG. 2. Similarly, the left end ofthe valve spool has a cylindrical lano 221a which sealingly engages themain bore to the left of the return passage 136a and which is sealinglyengageable with the bore land 204a between passages 202a and 136a whenthe spool is displaced axially to the right from the neutral positionshown in FIG. 2.

The centering spring assembly for the valve spool includes a coil spring143 engaged under compression between a pair of annular inner and outerwashers 144 and 145 which loosely encircle the reduced outer end 222 ofthe spool. The inner washer 144 engages an outwardly facing annularshoulder 223 on the valve spool. Washer 144 also engages the outer endof a sleeve 224, whose inner end engages a washer 225 which is clampedbetween the valve body and an end cap 226 enclosing the centering springassembly. The outer washer 14S engages a washer 227 clamped on the outerend of the spool, and it also abuts against an inwardly facing annularshoulder 220 on the end cap 226.

The bypass outlet port of the pressure-compensating valve is connectedto a bypass passage 230, which may be con nected either to thelow-pressure return line or to the inlet side of another load circuit,such as the inlet to a valve arrangement similar to the one shown inFIG. 2 and connected to operate an additional fluid motor in the samemanner. In this fashion, the excess flow into the firstpressure-compensating valve which is bypassed via port 120 may providethe inlet flow to a similar second valve arrangement.

OPERATION When the valve spool 112 is in its neutral position andassuming that the pump is off, spring 106 will position thepressure-compensating piston 114 as shown in FIG. 2, blocking the pumpoutput from the controlled flow outlet port 116 leading to the spoolvalve inlet and from the bypass outlet port 120.

In the neutral position of the valve spool, the spool valve referencepassage 202 is connected to the return passage 136 and the referencepassage 202a is connected to the return passage 136a. Consequently, thereference pressure chamber 124 of the pressure-compensating valve isconnected via passage 207, shuttle valve 206 and passages 205 and 205ato the return passages 136 and 136a of the spool valve. Consequently,the only pump pressure required to open the pressure-compensating valveis that necessary to overcome the biasing force of spring 106 on thepressure-compensating piston.

When the pump is turned on and the valve spool is shifted axially toconnect the inlet passage 200 to either motor passage 133 or 133a and toconnect the other motor passage to the adjacent return passage 136a or136, the motor passage which is conducting the inlet flow from the inletpassage 200 to the fluid motor will be connected to the correspondingreference passage 202 or 202a of the spool valve. At the same time, thevalve spool will block the adjacent return passage from this referencepassage. Consequently, the fluid pressure in the reference pressurechamber 124 of the pressure-compensating valve will now be substantiallyequal to the fluid pressure at the spool valve motor passage which isconducting the inlet flow. The pressure-compensating piston will respondto the pressure differential between the spool valve inlet passage 200and this motor passage to regulate the inlet flow rate through the spoolvalve by bypassing excess flow to the bypass outlet port 120 of thepressure-compensating valve and, if necessary, by restricting the flowfrom the inlet port 115 to the controlled flow port 116 leading to thespool valve inlet, as described.

LOAD CHECK OPERATION In both illustrated embodiments of the invention,the pressure-compensating piston (14 or 114) acts as a load check in theevent of a failure of the input pressure, such as by a failure of thepump or a break in the line connecting the pump output to the inlet port(15 or 115) of the pressure-compensating valve. In that event, theabsence of input pressure urging this piston to the right will enablethe bias spring (6 or 106) to move the'piston to the position shown inFIG. 1 or FIG. 2. With the controlled-flow outlet port (16 or 116) ofthe pressure-compensating valve blocked from both its inlet port (15 or115) and its bypass outlet port (20 or 120) by the pressurecompensatingpiston there can be no return of fluid through the spool valve and thepressure-compensating valve back to the break in the inlet line.

Iclaim:

1. A pressure-compensated flow control arrangement for controlling theoperation of a fluid motor comprising:

a spool valve having a bore, and an inlet passage, a motor passage and areturn passage intersecting said bore, and a valve spool movable in saidbore to control the fluid connections between said inlet passage andsaid motor passage and between said motor passage and said returnpassage, said valve spool having a neutral position blocking said motorpassage from both said inlet passage and said return passage, said valvespool being movable from said neutral position to a position connectingsaid inlet passage to said motor passage and blocking said motor passagefrom said return passage;

a pressure-compensating valve for regulating the inlet flow through saidspool valve, said pressure-compensating valve having an inlet port forconnection to the source of pressure fluid for the spool valve, a bypassport for bypassing pressure fluid away from said inlet passage of thespool valve, a reference pressure chamber, a pressurecompensating pistondisposed between said inlet and bypass ports to control the fluid flowtherebetween, said piston having oppositely facing surfaces which areexposed respectively to the fluid pressure at said inlet port and thefluid pressure at said reference pressure chamber, and spring meansbiasing said piston to a position blocking said bypass port from saidinlet port;

and connecting passage means including a shuttle valve for connectingsaid spool valve to said reference pressure chamber of thepressure-compensating valve;

said valve spool in its neutral position connecting said return passageto said reference pressure chamber through said connecting passagemeans;

and said valve spool, when displaced from said neutral position to aposition connecting said inlet passage to said motor passage, alsoconnecting said motor passage to said reference pressure chamber throughsaid connecting passage means.

2. A flow control arrangement according to claim 1 wherein saidconnecting passage means includes an internal longitudinal passage inthe valve spool, and transverse port means in the valve spool connectingsaid internal passage to said bore and registering with said returnpassage when the valve spool is in its neutral position, said transverseport means registering with said motor passage when the valve spool isdisplaced to a position connecting said inlet passage to said motorpassage and blocking said motor passage from said return passage.

3. A flow control arrangement according to claim 1, wherein saidconnecting passage means includes a reference passage intersecting saidspool valve bore between said motor passage and said return passage,said valve spool in its neutral position providing fluid communicationbetween said reference passage and said return passage, said valve spoolwhen displaced to said position connecting said inlet passage to saidmotor passage also providing fluid communication between said motorpassage and said reference passage, and said connecting passage meansalso includes a passage extending from said spool valve referencepassage to said reference pressure chamber of the pressure-compensatingvalve.

4. A flow control arrangement according to CLAIM 1, wherein saidpressure-compensating valve has a controlled flow outlet port connectedto said inlet passage of the spool valve, and sad spring means biasessaid piston to a position blocking said inlet port and said bypass portand said controlled flow outlet port from one another.

5. A flow control arrangement according to claim 4 wherein said inletport is disposed between said bypass port and said controlled flowoutlet port, and said piston has a pair of axially spaced lands whichrespectively block said bypass port and said controlled flow outletpassage from said inlet port in said last-mentioned position of thepiston.

6. A pressure-compensated directional flow control arrangement forcontrolling the operation of a reversible fluid motor comprising:

a spool valve having a bore, inlet passage means, a pair of motorpassages for connection to the opposite sides of the fluid motor, andreturn passages intersecting said bore, and a valve spool movable insaid bore to control the fluid connections between said inlet passagemeans and said motor passages and between said motor passages and saidreturn passages, said valve spool having a neutral position blockingboth said motor passages from said inlet passage means and from saidreturn passages, said valve spool being movable from said neutralposition to a position establishing an inlet flow passage between saidinlet passage means and a selected motor passage and establishing areturn flow passage between the other motor passage and thecorresponding return passage;

a pressure-compensating valve for regulating the inlet flow through saidspool valve, said pressure-compensating valve having an inlet port forconnection to the source of pressure fluid for the spool valve, a bypassport for bypassing pressure fluid away from said inlet passage means ofthe spool valve, a reference pressure chamber, a

piston slidably disposed between said inlet and bypass ports to controlthe fluid flow therebetween, said piston having oppositely facingsurfaces which are exposed respectively to the fluid pressure at saidinlet port and the fluid pressure at said reference pressure chamber,and spring means biasing said valve means to a position blocking saidbypass port from said inlet port;

and a shuttle valve connected between the spool valve and said referencepressure chamber of the pressure-compensating valve and operable, whenthe valve spool is posi' tioned to establish said inlet and returnpassages, to connect the motor passage which is in said inlet flowpassage to said reference pressure chamber;

said valve spool in said neutral position thereof blocking both motorpassages from said shuttle valve and connecting the return passages tosaid reference pressure chamber of the pressure-compensating valvethrough said shuttle valve.

7. A flow control arrangement according to claim 6,

wherein said shuttle valve is in thevalve spool.

8. A flow control arrangement according to claim 6, wherein:

said valve spool has a pair of longitudinal internal passages therein,and transverse port means connecting said internal passages to the spoolvalve bore and registrable selectively with said motor passages andreturn passages in different positions of the valve spool;

and said shuttle valve comprises a pair of oppositely facing valve seatsconnected to the respective internal passages of the valve spool, and amovable valve member reciprocably disposed between said valve seats forsealing engagement with either valve seat while spaced from the othervalve seat, and an outlet passage disposed between said valve seats forfluid communication with the valve seat from which the valve member isspaced, said outlet passage being connected to said reference pressurechamber of the pressure-compensating valve.

9. A flow control arrangement according to claim 8, wherein saidtransverse port means connect both internal spool passages to saidreturn passages when the valve spool is in said neutral position.

10 A flow control arrangement according to claim 6, wherein:

said spool valve has a pair of reference passages intersecting its borebetween the motor passages and the respective return passages;

said shuttle valve is connected between both said reference passages andthe reference pressure chamber of the pressure-compensating valve;

said valve spool in its neutral position connects said referencepassages to the respective return passages and blocks said referencepassages from the respective motor passages;

and said valve spool, when positioned to establish said inlet and returnflow passages through the spool valve, connects both said referencepassages to the respective motor passages.

ll. A pressure-compensated flow control arrangement for controlling theoperation ofa fluid motor comprising:

a flow control valve having inlet and motor ports and a lowpressurereturn passage, and selectively operable valve means in said controlvalve controlling the fluid communication between said ports andpassages, said valve means having a neutral position blocking said motorport from both said inlet port and said return passage, said valve meansbeing shiftable from said neutral position to a flow-conducting positionconnecting said inlet port to iii said motor port and providing a flowrestriction between them which varies with the position of said valvemeans;

a pressure-compensating valve connected ahead of the inlet port of saidcontrol valve to control the inlet flow thereto; saidpressure-compensating valve having one side thereof connected to saidmotor port and being operable to regulate the inlet flow to the controlvalve in accordance with rangement for controlling the operation of areversible fluid motor comprising: a

a spool valve having a bore, inlet passage means, a pair of motorpassages and a pair of return passages intersecting said bore, and avalve spool movable in said bore to control the fluid connectionsbetween said inlet passage means and said motor passages and betweensaid motor passages and said return passages;

said valve spool having a pair of longitudinal internal passages spacedapart axially of the spool therein and transverse port means connectingsaid internal passages to the spool valve bore, and a shuttle valve inthe spool operatively connected between said internal passages andexposed to the fluid pressure in each, said shuttle valve comprising apair of oppositely facing valve seats connected individually to therespective internal passages of the spool, a movable valve memberreciprocably disposed between said valve seats for sealing engagementwith either valve seat while spaced from the other valve seat, and anoutlet passage disposed between said valve seats for fluid communicationwith the valve seat from which the valve member is spaced, saidtransverse port means connecting both internal passages of the valvespool to said return passages when the valve spool is in a neutralposition blocking said inlet passage means from said motor passages,

said valve spool means being shiftable longitudinally to connect saidinlet passage means to a selected one of said motor passages and toconnect the other of said motor passages to a return passage and toconnect the motor passages to the respective internal passages in thevalve spool through said transverse port: means therein;

a pressure-compensating valve for regulating the inlet flow through saidspool valve, said pressure-compensating valve having an inlet port forconnection to the source of pressure fluid for the spool valve, a bypassport for bypassing pressure fluid away from said inlet passage means ofthe spool valve, a reference pressure chamber, a piston slidablydisposed between said inlet and bypass port to control the fluid flowtherebetween, said piston having oppositely facing surfaces which areexposed respectively to the fluid pressure at said inlet port and thefluid pressure at said reference pressure chamber, spring means biasingsaid valve means to a position blocking said bypass port from said inletport, and passage means connecting said reference pressure chamber tosaid shuttle valve in the spool to apply to said reference pressurechamber the fluid pressure in the longitudinal internal passage which isin communication with the valve seat which is spaced from said valvemember.

1. A pressure-compensated flow control arrangement for controlling theoperation of a fluid motor comprising: a spool valve having a bore, andan inlet passage, a motor passage and a return passage intersecting saidbore, and a valve spool movable in said bore to control the fluidconnections between said inlet passage and said motor passage andbetween said motor passage and said return passage, said valve spoolhaving a neutral position blocking said motor passage from both saidinlet passage and said return passage, said valve spool being movablefrom said neutral position to a position connecting said inlet passageto said motor passage and blocking said motor passage from said returnpassage; a pressure-compensating valve for regulating the inlet flowthrough said spool valve, said pressure-compensating valve having aninlet port for connection to the source of pressure fluid for the spoolvalve, a bypass port for bypassing pressure fluid away from said inletpassage of the spool valve, a reference pressure chamber, apressure-compensating piston disposed between said inlet and bypassports to control the fluid flow therebetween, said piston havingoppositely facing surfaces which are exposed respectively to the fluidpressure at said inlet port and the fluid pressure at said referencepressure chamber, and spring means biasing said piston to a positionblocking said bypass port from said inlet port; and connecting passagemeans including a shuttle valve for connecting said spool valve to saidreference pressure chamber of the pressure-compensating valve; saidvalve spool in its neutral position connecting said return passage tosaid reference pressure chamber through said connecting passage means;and said valve spool, when displaced from said neutral position to aposition connecting said inlet passage to said motor passage, alsoconnecting said motor passage to said reference pressure chamber throughsaid connecting passage means.
 2. A flow control arrangement accordingto claim 1 wherein said connecting passage means includes an internallongitudinal passage in the valve spool, and transverse port means inthe valve spool connecting said internal passage to said bore andregistering with said return passage when the valve spool is in itsneutral position, said transverse port means registering with said motorpassage when the valve spool is displaced to a position connecting saidinlet passage to said motor passage and blocking said motor passage fromsaid return passage.
 3. A flow control arrangement according to claim 1,wherein said connecting passage means includes a reference passageintersecting said spool valve bore between said motor passage and saidreturn passage, said valve spool in its neutral position providing fluidcommunication between said reference passage and said return passage,said valve spool when displaced to said position connecting said inletpassage to said motor passage also providing fluid communication betweensaid motor passage and said reference passage, and said connectingpassage means also includes a passage extending from said spool valvereference passage to said reference pressure chamber of thepressure-compensating valve.
 4. A flow control arrangement according toCLAIM 1, wherein said pressure-compensating valve has a controlled flowoutlet port connected to said inlet passage of the spool valve, and sadspring means biases said piston to a position blocking said inlet portand said bypass port and said controlled flow outlet port from oneanother.
 5. A flow control arrangement according to claim 4 wherein saidinlet port is disposed between said bypass port and said controlled flowoutlet port, and said piston has a pair of axially spaced lands whichrespectively block said bypass port and said controlled flow outletpassage from said inlet port in said last-mentioned position of thepiston.
 6. A pressure-compensated directional flow control arrangementfor controlling the operation of a reversible fluid motor comprising: aspool valve having a bore, inlet passage means, a pair of motor passagesfor connection to the opposite sides of the fluid motor, and returnpassages intersecting said bore, and a valve spool movable in said boreto control the fluid connections between said inlet passage means andsaid motor passages and between said motor passages and said returnpassages, said valve spool having a neutral position blocking both saidmotor passages from said inlet passage means and from said returnpassages, said valve spool being movable from said neutral position to aposition establishing an inlet flow passage between said inlet passagemeans and a selected motor passage and establishing a return flowpassage between the other motor passage and the corresponding returnpassage; a pressure-compensating valve for regulating the inlet flowthrough said spool valve, said pressure-compensating valve having aninlet port for connection to the source of pressure fluid for the spoolvalve, a bypass port for bypassing pressure fluid away from said inletpassage means of the spool valve, a reference pressure chamber, a pistonslidably disposed between said inlet and bypass ports to control thefluid flow therebetween, said piston having oppositely facing surfaceswhich are exposed respectively to the fluid pressure at said inlet portand the fluid pressure at said reference pressure chamber, and springmeans biasing said valve means to a position blocking said bypass portfrom said inlet port; and a shuttle valve connected between the spoolvalve and said reference pressure chamber of the pressure-compensatingvalve and operable, when the valve spool is positioned to establish saidinlet and return passages, to connect the motor passage which is in saidinlet flow passage to said reference pressure chamber; said valve spoolin said neutral position thereof blocking both motor passages from saidshuttle valve and connecting the return passages to said referencepressure chamber of the pressure-compensating valve through said shuttlevalve.
 7. A flow control arrangement according to claim 6, wherein saidshuttle valvE is in the valve spool.
 8. A flow control arrangementaccording to claim 6, wherein: said valve spool has a pair oflongitudinal internal passages therein, and transverse port meansconnecting said internal passages to the spool valve bore andregistrable selectively with said motor passages and return passages indifferent positions of the valve spool; and said shuttle valve comprisesa pair of oppositely facing valve seats connected to the respectiveinternal passages of the valve spool, and a movable valve memberreciprocably disposed between said valve seats for sealing engagementwith either valve seat while spaced from the other valve seat, and anoutlet passage disposed between said valve seats for fluid communicationwith the valve seat from which the valve member is spaced, said outletpassage being connected to said reference pressure chamber of thepressure-compensating valve.
 9. A flow control arrangement according toclaim 8, wherein said transverse port means connect both internal spoolpassages to said return passages when the valve spool is in said neutralposition. 10 A flow control arrangement according to claim 6, wherein:said spool valve has a pair of reference passages intersecting its borebetween the motor passages and the respective return passages; saidshuttle valve is connected between both said reference passages and thereference pressure chamber of the pressure-compensating valve; saidvalve spool in its neutral position connects said reference passages tothe respective return passages and blocks said reference passages fromthe respective motor passages; and said valve spool, when positioned toestablish said inlet and return flow passages through the spool valve,connects both said reference passages to the respective motor passages.11. A pressure-compensated flow control arrangement for controlling theoperation of a fluid motor comprising: a flow control valve having inletand motor ports and a low-pressure return passage, and selectivelyoperable valve means in said control valve controlling the fluidcommunication between said ports and passages, said valve means having aneutral position blocking said motor port from both said inlet port andsaid return passage, said valve means being shiftable from said neutralposition to a flow-conducting position connecting said inlet port tosaid motor port and providing a flow restriction between them whichvaries with the position of said valve means; a pressure-compensatingvalve connected ahead of the inlet port of said control valve to controlthe inlet flow thereto; said pressure-compensating valve having one sidethereof connected to said motor port and being operable to regulate theinlet flow to the control valve in accordance with the pressuredifferential across said flow restriction when said valve means in thecontrol valve is in a flow-conducting position; saidpressure-compensating valve having one side thereof connected to saidreturn passage when said valve means in the flow control valve is insaid neutral position; and a shuttle valve interposed said one side ofsaid pressure-compensating valve and said flow control valve.
 12. Apressure-compensated directional flow control arrangement forcontrolling the operation of a reversible fluid motor comprising: aspool valve having a bore, inlet passage means, a pair of motor passagesand a pair of return passages intersecting said bore, and a valve spoolmovable in said bore to control the fluid connections between said inletpassage means and said motor passages and between said motor passagesand said return passages; said valve spool having a pair of longitudinalinternal passages spaced apart axially of the spool therein andtransverse port means connecting said internal passages to the spoolvalve bore, and a shuttle valve in the spool operatively connectedbetween said internal passages and exposed to the fluid pressure ineach, said shuttle valve compRising a pair of oppositely facing valveseats connected individually to the respective internal passages of thespool, a movable valve member reciprocably disposed between said valveseats for sealing engagement with either valve seat while spaced fromthe other valve seat, and an outlet passage disposed between said valveseats for fluid communication with the valve seat from which the valvemember is spaced, said transverse port means connecting both internalpassages of the valve spool to said return passages when the valve spoolis in a neutral position blocking said inlet passage means from saidmotor passages, said valve spool means being shiftable longitudinally toconnect said inlet passage means to a selected one of said motorpassages and to connect the other of said motor passages to a returnpassage and to connect the motor passages to the respective internalpassages in the valve spool through said transverse port means therein;a pressure-compensating valve for regulating the inlet flow through saidspool valve, said pressure-compensating valve having an inlet port forconnection to the source of pressure fluid for the spool valve, a bypassport for bypassing pressure fluid away from said inlet passage means ofthe spool valve, a reference pressure chamber, a piston slidablydisposed between said inlet and bypass port to control the fluid flowtherebetween, said piston having oppositely facing surfaces which areexposed respectively to the fluid pressure at said inlet port and thefluid pressure at said reference pressure chamber, spring means biasingsaid valve means to a position blocking said bypass port from said inletport, and passage means connecting said reference pressure chamber tosaid shuttle valve in the spool to apply to said reference pressurechamber the fluid pressure in the longitudinal internal passage which isin communication with the valve seat which is spaced from said valvemember.